A variety of microbial decontamination processes employ sterilizing vapors, such as steam or a mixture of water vapor with another antimicrobial (e.g., hydrogen peroxide vapor), in relatively large quantities. Steam sterilizers, for example, employ pressurized high temperature dry steam as a sterilizing vapor. Dry steam is preferred, as unvaporized water droplets can shield microbes or prions from the steam. Hydrogen peroxide vapor systems use a flow of hydrogen peroxide vapor, typically at around atmospheric pressure or below. Again, the presence of water droplets is not beneficial, as they can shield microbes and prions from the peroxide vapor.
Medical, pharmaceutical, dental, and food packaging items are often sterilized prior to use or reuse, in such systems. Vapors are also used in the decontamination of sterile enclosures and other clean rooms used by hospitals and laboratories. Processing equipment for pharmaceuticals and food, freeze driers, and meat processing equipment are also advantageously disinfected or sterilized with a vapor.
In the case of steam, for example, microbial decontamination systems often create the steam by boiling water inside a reservoir of a steam generator, such as a boiler. A large heating element is usually located over the bottom surface of the reservoir to maintain a supply of boiling water.
In the case of other water-based antimicrobial vapors, such as hydrogen peroxide vapor, a vaporizer outside the chamber generates a flow of vapor. Typically, a solution of about 35% hydrogen peroxide in water is injected into the vaporizer as fine droplets or a mist through injection nozzles. The droplets contact a heated surface which heats the droplets to form the vapor, without breaking the hydrogen peroxide down to water and oxygen. A carrier gas is circulated over the heat transfer surface to absorb the peroxide vapor.
Such vapor generation methods have disadvantages when large quantities of vapor are desired or vapor is needed at short notice. Boilers tend to be relatively large pieces of equipment, which work best when the wattage is spread out over a large heating element surface area. This keeps the watt density low and extends the life of the heating element. The large heating element surface area, however, takes up considerable space. Additionally, to avoid damage to the heating element, it is completely immersed in water. Thus, it takes some time to heat the large volume of water to steam temperature in order for steam generation to begin. It is expensive to maintain a supply of over 100° C. water ready for a demand. Any unused heated water generally has to be cooled in a heat exchanger before it is disposed of in a municipal waste water system.
Vaporized hydrogen peroxide is a particularly useful vapor sterilant for both vacuum sterilizing systems and rooms and other large enclosures. It is effective at or close to room temperature, which reduces the potential for thermal degradation of associated equipment and items to be sterilized or disinfected within the sterilizer enclosure. In addition, hydrogen peroxide readily decomposes to water and oxygen, thus simplifying disposal.
As the size of the sterilizer or enclosure increases, or the demand for hydrogen peroxide is increased, the efficiency of the vaporization system becomes more significant. The capacity of the vaporizer is limited in a number of ways. First, the vaporization process creates a pressure increase, reducing the flow of the carrier gas through the vaporizer. Second, to maintain sterilization efficiency, the pressure at which the vapor is generated is limited to that at which the hydrogen peroxide is stable in the vapor state. Third, the time taken to generate the hydrogen peroxide is dependent on the time taken to heat a surface to the vaporization temperature of hydrogen peroxide.
One solution has been to increase the size of the vaporizer, the injection rate of hydrogen peroxide into the vaporizer, and the flow rate of carrier gas. However, the carrier gas tends to cool the heating surface, disrupting the vaporization process. Heating the surface to a higher temperature breaks down the hydrogen peroxide.
Yet another solution is to use multiple vaporizers to feed a single enclosure. The vaporizers may each be controlled independently, to allow for variations in chamber characteristics. However, the use of multiple vaporizers adds to the cost of the system and requires careful monitoring to ensure that each vaporizer is performing with balanced efficiency. None of these solutions addresses the initial warm up time needed for raising the temperature of the vaporizer to the vaporization temperature.
The present invention provides new and improved vaporization systems and methods which overcome the above-referenced problems and others.